The mobile network, such as the global system for mobile communications (GSM) and the universal mobile telecommunications system (UMTS) etc., adopts a circuit switched technology, named as circuit switched (CS for short) domain, which can provide a basic voice service and some complementary services based on the voice service to the user.
In some places of the world such as Africa, South America and South Asia, etc., a lack of rapid and reliable transmission resources or the high transmission cost brings the operator with some difficulty in the network and service deployment. However, according to the statistic data, most calls in the mobile network are local calls in those places, and these calls are generated in the same base station system (BSS). For the local call, if the local exchange technology is adopted (the voice data is looped at the BSS), then the A port transmission resource between the BSS and a mobile switch center (MSC) of the core network is saved.
FIG. 1 is a diagram of a traditional voice call, a user equipment (UE) accesses the BSS and the MSC through the circuit switched domain. When a UE1 calls a UE2, the UE1 sends a call setup request to its accessed MSC through the BSS; the MSC finds the called UE2 according to an accessing location information of UE2, and notifies the BSS to establish a radio bearer connected to the UE1 and the UE2, and establish the bearers of the UE1 and the UE2 between the BSS and the MSC respectively; the two side bearers of the MSC are looped, so as to ensure a voice communication between the UE1 and the UE2.
FIG. 2 is a diagram of a voice call using the local call and local exchange technology, compared with FIG. 1, when the MSC receives the call setup request of the UE1, the MSC judges whether the UE1 and the UE2 belong to one same BSS according to a cell; if the UE1 and the UE2 belong to one same BSS, then the MSC notifies the BSS to execute the local exchange; the bearer loop of the UE1 and the UE2 is executed at the BSS side, thus the bearer resources between the BSS and the MSS are saved.
FIG. 3 is a signaling flow of using the local call and local exchange technology in FIG. 2, including the following steps:
in step 301, the UE1 and the UE2 initiate a call under the same BSS, and establish the interconnection through a core network, and the MSC assigns a circuit number or a call identifier between the BSS and the MSC for the calling UE1 and the called UE2;
in step 302, the called UE2 replies in the ringing status, and sends a called reply message to the MSC through the BSS;
in step 303, the MSC sends the called reply message to the calling UE1, and notifies the UE1 of call connecting;
in step 304, the MSC judges whether the current call is a local call belonged to one same BSS according to the present location information of the calling UE1 and the called UE2;
in step 305, if being a local call belonged to one same BSS, then the MSC sends a local exchange command message to the BSS, and notifies the BSS to execute the local exchange, and the local exchange command message includes the circuit number or the call identifier between the BSS and the MSC assigned for the calling UE1 and the called UE2 by the MSC in step 301;
in step 306, the BSS receives the local exchange command message, associates to two ongoing communication sessions according to the circuit number or the call identifier of the calling or the called in the local exchange command message, and performs the loop on its voice data bearer, so as to realize the exchange of the voice bearer inside the BSS;
in step 307, after the local exchange succeeds, the BSS sends a local exchange success message to the MSC;
in step 308, the MSC, after receiving the local exchange success message, notifies the BSS to release the voice bearer connection between the BSS and the MSC.
According to the analysis of the above steps, if in the case that one BSS connects with a plurality of MSCs, as shown in FIG. 4, the calling UE1 accesses a MSC1 through the BSS, and the called UE2 accesses a MSC2 through the BSS. Although the calling and the called initiate a call in one same BSS, the calling and the called access the different MSCs respectively, thus causing the problem that no matter the MSC1 accessed by the calling UE1, or the MSC2 accessed by the called UE2 shown in step 304 is unable to judge whether the current call is a local call according to the location information of the calling and the called, and finally causing the problem that the local call is unable to execute the local exchange.